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From: ebiederm@xmission.com (Eric W. Biederman)
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Oleg Nesterov <oleg@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Kees Cook <keescook@chromium.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"the arch\/x86 maintainers" <x86@kernel.org>,
	H Peter Anvin <hpa@zytor.com>
Subject: Re: [PATCH v2 10/32] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved.
Date: Mon, 25 Oct 2021 16:28:22 -0500	[thread overview]
Message-ID: <87k0i0x095.fsf@disp2133> (raw)
In-Reply-To: <CAHk-=whS0PL0NZrz2d8a3V+8=4szSZ6jqkg5fkjeaEjMN_NX8Q@mail.gmail.com> (Linus Torvalds's message of "Mon, 25 Oct 2021 14:12:03 -0700")

Linus Torvalds <torvalds@linux-foundation.org> writes:

> On Mon, Oct 25, 2021 at 1:54 PM Eric W. Biederman <ebiederm@xmission.com> wrote:
>>
>> Update save_v86_state to always complete all of it's work except
>> possibly some of the copies to userspace even if save_v86_state takes
>> a fault.  This ensures that the kernel is always in a sane state, even
>> if userspace has done something silly.
>
> Well, honestly, with this change, you might as well replace the
> force_sigsegv() with just a plain "force_sig()", and make it something
> the process can catch.

The trouble is I don't think there is enough information made available
for user space to do anything with the SIGSEGV.  My memory is that
applications like dosemu very much have a SIGSEGV handler.

So I think if it ever happened it could be quite confusing.  Not to
mention the pr_alert message.

But I guess if a test is written like you suggest we can include enough
information for someone to make sense of things.

> The only thing that "force_sigsgv()" does is to make SIGSEGV
> uncatchable. In contrast, a plain "force_sig()" just means that it
> can't be ignored - but it can be caught, and it is fatal only when not
> caught.
>
> And with the "always complete the non-vm86 state restore" part change,
> there's really no reason for it to not be caught.
>
> Of course, the other case (where we have no state information for the
> "enter vm86 mode" case) is still fatal, and is a "this should never
> happen". But the "cannot write to the vm86 save state" thing isn't
> technically fatal.
>
> It should even be possible to write a test for it: passing a read-only
> pointer to the vm86() system call. The vm86 entry will work (because
> it only reads the vm86 state from it), but then at vm86 exit, writing
> the state back will fail.
>
> Anybody?

I am enthusiastic about writing a test, but I will plod in that
direction just so I can get this sorted out.

Eric

  reply	other threads:[~2021-10-25 21:28 UTC|newest]

Thread overview: 95+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-20 17:32 [PATCH 00/20] exit cleanups Eric W. Biederman
2021-10-20 17:43 ` [PATCH 01/20] exit/doublefault: Remove apparently bogus comment about rewind_stack_do_exit Eric W. Biederman
2021-10-21 16:02   ` Kees Cook
2021-10-20 17:43 ` [PATCH 02/20] exit: Remove calls of do_exit after noreturn versions of die Eric W. Biederman
2021-10-21 16:02   ` Kees Cook
2021-10-21 16:25     ` Eric W. Biederman
2021-10-20 17:43 ` [PATCH 03/20] reboot: Remove the unreachable panic after do_exit in reboot(2) Eric W. Biederman
2021-10-21 16:05   ` Kees Cook
2021-10-20 17:43 ` [PATCH 04/20] signal/sparc32: Remove unreachable do_exit in do_sparc_fault Eric W. Biederman
2021-10-21 16:05   ` Kees Cook
2021-10-20 17:43 ` [PATCH 05/20] signal/mips: Update (_save|_restore)_fp_context to fail with -EFAULT Eric W. Biederman
2021-10-21 16:06   ` Kees Cook
2021-10-24  4:24   ` Maciej W. Rozycki
2021-10-25 20:55     ` Eric W. Biederman
2021-10-24 15:27   ` Thomas Bogendoerfer
2021-10-20 17:43 ` [PATCH 06/20] signal/sh: Use force_sig(SIGKILL) instead of do_group_exit(SIGKILL) Eric W. Biederman
2021-10-20 19:57   ` Linus Torvalds
2021-10-27 14:24     ` Rich Felker
2021-10-21 16:08   ` Kees Cook
2021-10-20 17:43 ` [PATCH 07/20] signal/powerpc: On swapcontext failure force SIGSEGV Eric W. Biederman
2021-10-21 16:09   ` Kees Cook
2021-10-20 17:43 ` [PATCH 08/20] signal/sparc: In setup_tsb_params convert open coded BUG into BUG Eric W. Biederman
2021-10-21 16:12   ` Kees Cook
2021-10-20 17:43 ` [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON Eric W. Biederman
2021-10-21 16:15   ` Kees Cook
2021-11-12 15:40   ` Eric W. Biederman
2021-11-12 17:51     ` Brian Gerst
2021-11-12 19:57       ` Eric W. Biederman
2021-11-12 20:40         ` Linus Torvalds
2021-11-12 21:03           ` Eric W. Biederman
2021-11-12 21:23             ` Linus Torvalds
2021-11-12 21:24               ` Linus Torvalds
2021-11-12 21:37                 ` [GIT PULL ] signal/vm86_32: Remove pointless test in BUG_ON Eric W. Biederman
2021-11-13 19:15                   ` pr-tracker-bot
2021-11-12 21:43                 ` [PATCH 09/20] signal/vm86_32: Replace open coded BUG_ON with an actual BUG_ON Eric W. Biederman
2021-10-20 17:43 ` [PATCH 10/20] signal/vm86_32: Properly send SIGSEGV when the vm86 state cannot be saved Eric W. Biederman
2021-10-21 16:16   ` Kees Cook
2021-10-21 17:02     ` Eric W. Biederman
2021-10-21 20:33       ` Kees Cook
2021-10-21 23:08   ` Andy Lutomirski
2021-10-24 16:06     ` Eric W. Biederman
     [not found]   ` <875ytkygfj.fsf_-_@disp2133>
2021-10-25 21:12     ` [PATCH v2 10/32] " Linus Torvalds
2021-10-25 21:28       ` Eric W. Biederman [this message]
2021-10-25 22:25     ` Andy Lutomirski
2021-10-25 23:45       ` Linus Torvalds
2021-10-26  0:21         ` Andy Lutomirski
2021-10-20 17:43 ` [PATCH 11/20] signal/s390: Use force_sigsegv in default_trap_handler Eric W. Biederman
2021-10-21 16:17   ` Kees Cook
2021-10-26  9:38   ` Christian Borntraeger
2021-10-28 15:56     ` Eric W. Biederman
2021-10-29 19:32       ` Eric W. Biederman
2021-10-20 17:43 ` [PATCH 12/20] exit/kthread: Have kernel threads return instead of calling do_exit Eric W. Biederman
2021-10-21 11:12   ` Christoph Hellwig
2021-10-21 15:11     ` Eric W. Biederman
2021-10-21 16:21   ` Kees Cook
2021-10-20 17:43 ` [PATCH 13/20] signal: Implement force_fatal_sig Eric W. Biederman
2021-10-20 20:05   ` Linus Torvalds
2021-10-20 21:25     ` Eric W. Biederman
2021-10-25 22:41     ` Andy Lutomirski
2021-10-25 23:15       ` Linus Torvalds
2021-10-26  4:45         ` Eric W. Biederman
2021-10-26  4:57         ` Eric W. Biederman
2021-10-26 16:15           ` Linus Torvalds
2021-10-28 16:33             ` Eric W. Biederman
2021-10-21 16:24   ` Kees Cook
2021-10-21 16:33     ` Eric W. Biederman
2021-10-21 16:39       ` Kees Cook
2021-10-20 17:44 ` [PATCH 14/20] exit/syscall_user_dispatch: Send ordinary signals on failure Eric W. Biederman
2021-10-21 16:25   ` Kees Cook
2021-10-21 16:37     ` Eric W. Biederman
2021-10-21 16:40       ` Kees Cook
2021-10-21 17:05         ` Eric W. Biederman
2021-10-25 22:32     ` Andy Lutomirski
2021-10-21 16:35   ` Gabriel Krisman Bertazi
2021-10-20 17:44 ` [PATCH 15/20] signal/sparc32: Exit with a fatal signal when try_to_clear_window_buffer fails Eric W. Biederman
2021-10-21 16:34   ` Kees Cook
2021-10-21 16:56     ` Eric W. Biederman
2021-10-20 17:44 ` [PATCH 16/20] signal/sparc32: In setup_rt_frame and setup_fram use force_fatal_sig Eric W. Biederman
2021-10-21 16:34   ` Kees Cook
2021-10-20 17:44 ` [PATCH 17/20] signal/x86: In emulate_vsyscall force a signal instead of calling do_exit Eric W. Biederman
2021-10-21 16:36   ` Kees Cook
2021-10-20 17:44 ` [PATCH 18/20] exit/rtl8723bs: Replace the macro thread_exit with a simple return 0 Eric W. Biederman
2021-10-21  7:06   ` Greg KH
2021-10-21 15:06     ` Eric W. Biederman
2021-10-21 16:37   ` Kees Cook
2021-10-20 17:44 ` [PATCH 19/20] exit/rtl8712: " Eric W. Biederman
2021-10-21  7:07   ` Greg KH
2021-10-21 16:37   ` Kees Cook
2021-10-20 17:44 ` [PATCH 20/20] exit/r8188eu: " Eric W. Biederman
2021-10-21  7:07   ` Greg KH
2021-10-21 16:37   ` Kees Cook
2021-10-20 21:51 ` [PATCH 21/20] signal: Replace force_sigsegv(SIGSEGV) with force_fatal_sig(SIGSEGV) Eric W. Biederman
2021-10-21  8:09   ` Geert Uytterhoeven
2021-10-21 13:33     ` Eric W. Biederman
2021-10-21  8:32   ` Philippe Mathieu-Daudé

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